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This idea was already encountered in chapter 2 where the notion of field operators developing non-zero expectation values in the vacuum state (VEV) indicated a non-trivial structure of the vacuum. In fact, already the concept of 0-point energy within the context of QM invoked the same picture. In chapter 3 the idea of vacuum energy per se was introduced to explain recent experimental data (this idea of vacuum energy in fact going back to Einstein in the year 1917). Chapter 4 connected the VEV, the vacuum energy and the cosmological constant by virtue of a tachyonic mass parameter

$\displaystyle v = \frac{\mu}{\sqrt{\lambda_H}}$   and$\displaystyle \qquad \rho = \frac{\mu^4}{4 \lambda_H}.$ (A.2)

In effect the whole issue of vacuum energy can be traced back to a specific potential for a tachyon scalar field $ \phi$. String/M-theory also gave a link between the VEV of the scalar dilaton and the cosmological constant, recall note [].

jbg 2002-05-26